Steam turbine rotating blade of 52 inch active length for steam turbine low pressure application

Abstract

A bucket for use in the low-pressure section of a steam turbine engine is provided. The bucket has a vane length of at least about 52 inches. The bucket is comprised of a dovetail section disposed near an inner radial position of the bucket, a tip shroud disposed near an outer radial position of the bucket and a part span shroud disposed at an intermediate radial position. The intermediate radial position is disposed at a location between the inner and outer radial positions the intermediate radial positioning adapted to promote aerodynamic performance of the part span shroud. The bucket is comprised of a chromium steel.

What is claimed is: 
     
       1. A bucket for use in the low pressure section of a steam turbine, the bucket being formed with a vane length of at least about 52 inches and comprising:
 a dovetail section disposed near an inner radial position of the bucket; 
 a tip shroud disposed near an outer radial position of the bucket; 
 a part span shroud disposed at an intermediate radial position and comprising a wing shaped aerodynamic airfoil, the intermediate radial position located between the inner and outer radial positions on a suction side and a pressure side of the vane; and 
 wherein the bucket is comprised of a chromium-stainless alloy. 
 
     
     
       2. The bucket according to  claim 1 , wherein the dovetail section is comprised of a curved, axial-entry dovetail. 
     
     
       3. The bucket according to  claim 1 , wherein the curved, axial-entry dovetail includes four hooks. 
     
     
       4. The bucket according to  claim 1 , wherein the curved, axial-entry dovetail includes an axial retention element adapted to receive a split lockwire to prevent axial movement of the bucket within. 
     
     
       5. The bucket according to  claim 1 , wherein the bucket comprises a last stage bucket. 
     
     
       6. The bucket according to  claim 1 , wherein the part span shroud is disposed for aerodynamic performance at approximately 46% of vane length between the inner radial position and the outer radial position. 
     
     
       7. The bucket according to  claim 1 , wherein the wing shaped aerodynamic airfoil of the part span shroud includes a substantially constant profile presented to steam flow from root end to tip end. 
     
     
       8. The bucket according to  claim 1 , wherein a leading edge is flame hardened. 
     
     
       9. A steam turbine comprising a low pressure turbine section, the low pressure turbine section comprising:
 a plurality of last stage buckets arranged about a turbine wheel, the plurality of last stage buckets having a vane length of about 52 inches or greater, at least one last stage bucket comprising: 
 a dovetail section disposed near an inner radial position of the at least one last stage bucket; 
 a tip shroud disposed near an outer radial position of the at least one last stage bucket; 
 a part span shroud disposed at an intermediate radial position, the intermediate radial position located between the inner and outer radial positions, and the intermediate radial positioning being adapted to promote aerodynamic performance of the part span shroud; 
 wherein the part span shrouds of the plurality of last stage buckets are configured to have a gap between a part span shroud of an adjacent last stage bucket; and 
 wherein each of the plurality of last stage buckets are comprised of a chromium-stainless alloy. 
 
     
     
       10. The steam turbine according to  claim 9 , wherein the plurality of last stage buckets comprise an exit annulus area of about 172 ft 2  or more. 
     
     
       11. The steam turbine according to  claim 9 , wherein a the plurality of last stage buckets rotate at an operating speed of about 1,800 rpm. 
     
     
       12. The steam turbine according to  claim 9 , wherein the tip shrouds of the plurality of last stage buckets are configured to have a gap between a tip shroud of an adjacent last stage bucket, and wherein the gap is closed as the turbine wheel rotates above a predetermined speed and the plurality of last stage buckets untwist due to the rotation of the turbine wheel. 
     
     
       13. The steam turbine according to  claim 9 , wherein the gap is closed as the turbine wheel rotates above a predetermined speed and the last stage buckets untwist due to the rotation of the turbine wheel. 
     
     
       14. The steam turbine according to  claim 9 , wherein the wherein the part span shroud is disposed for aerodynamic performance at approximately 46% of vane length between the inner radial position and the outer radial position. 
     
     
       15. The steam turbine according to  claim 14 , wherein the part span shroud comprises a wing shaped aerodynamic airfoil. 
     
     
       16. The steam turbine according to  claim 15 , wherein the wing shaped aerodynamic airfoil includes a substantially constant profile presented to steam flow from root end to tip end. 
     
     
       17. The steam turbine according to  claim 9 , wherein the dovetail section comprises a curved, axial-entry dovetail. 
     
     
       18. The steam turbine according to  claim 17 , wherein the curved, axial-entry dovetail includes four hooks. 
     
     
       19. The steam turbine according to  claim 18 , wherein the curved, axial-entry dovetail includes an axial retention element adapted to receive a split lockwire to prevent axial movement of the bucket within. 
     
     
       20. A steam turbine comprising a low pressure turbine section, the low pressure turbine section comprising:
 a plurality of last stage buckets arranged about a turbine wheel, the plurality of last stage buckets having a vane length of about 52 inches or greater, at least one last stage bucket comprising: 
 a dovetail section disposed near an inner radial position of the at least one last stage bucket; 
 a tip shroud disposed near an outer radial position of the at least one last stage bucket; 
 a part span shroud disposed at an intermediate radial position, the intermediate radial position located between the inner and outer radial positions, and the intermediate radial positioning being adapted to promote aerodynamic performance of the part span shroud; and 
 wherein the part span shroud comprises a wing shaped aerodynamic airfoil having a substantially constant profile presented to steam flow from root end to tip end.